1. Field of the Invention
The present invention relates to a solar cell manufacturing method.
2. Prior Art
A solar cell is generally provided with electrodes for outputting the generated electromotive force and with an antireflection coating for reducing energy loss due to the reflection of light incident to the cell. In conventional methods of manufacturing solar cells, the antireflection coating is applied after the formation of the electrodes (except in those cases where exceptional kinds of materials are used). The reason is that, generally, the coating materials are electrically highly-resistive, and therefore the formation of electrodes after the application of the coating causes the resistance of the electrodes to be extremely high, making the product impractical. It is known that, when the antireflection coating is made of titanium oxide, the process of baking electrodes provided on the coating will break the coating at those parts to contact with the electrodes, causing the latter to contact the wafer. However, such a method can not be used for most coating materials other than titanium oxide.
The electrodes, which are formed usually by means of printing, plating, or evaporation, conventionally are coated with solder to improve the weather resistance and reliability of the solar cell and to enable lead wires to be easily connected. Therefore, the process of applying the antireflection coating must be carried out at a temperature below 180.degree. C., the melting point of solder. The plasma CVD (chemical vapor deposition) method, one of the conventional methods of coating, has also been employed at a temperature not exceeding the melting point of solder. However, this process temperature requirement results in a disadvantage, especially when using silicon nitride as a coating material. Silicon nitride is deposited in the form of a film on a solar cell element by means of the plasma CVD method. The application of a silicon nitride film makes the surface of the cell element inactive, resulting in a decrease in the recombination rate of minority carriers produced by the irradiation of light, and the electrical characteristics of the solar cell are thus improved. Besides, this phenomenon has been found more remarkable when silicon nitride is deposited at higher temperatures. Therefore, the above low process temperature requirements accompanying the conventional technology present an important disadvantage in the application of an antireflection coating.